Thudding noise in chest when breathing out hard?

I have bronchiectasis and have noticed recently that when I force air out for my huffing exercise I feel and hear a thudding in the centre of my chest. I am on seretide accuhaler and have been for 6 months. I am constantly coughing since having my gall bladder surgery in may of this year and not been well since. Cant see my lung specialist till december. So is this a normal sound as I have never been aware of this before